Lightning strikes - among 3000 to hit the state - have set a house on fire and blown the roof off another in separate incidents in Melbourne's suburbs.

It has literally blown a tiled roof off a first floor extension.

A home in Berwick was mostly destroyed when a bolt of lightning hit the roof and set it ablaze about 9.20am on Tuesday, while a woman and child were taken to hospital after their home in Thornbury also took a direct hit.